THE CHEMISTRY OE THE ANIMAL BODY. 561 



Carbohydrates. 



The important sugar of the blood and the tissues is dextrose. It is 

 derived from the hydration of starchy foods, and from proteid metabolism. 

 From dextrose the lactic glands probably manufacture another carbohydrate, 

 milk-sugar. Cane-sugar forms an article highly prized as a food. Thestudy 

 of the various sugars or carbohydrates is of especial interest, because their 

 chemical nature is now well known. 



Carbohydrates were formerly denned as bodies which, like the sugars and 

 substances of allied constitution, contain carbon, hydrogen, and oxygen, the 

 carbon atoms being present to the number of six or multiples thereof, the 

 hydrogen and oxygen being present in a proportion to form water. Glycoses 

 include the monosaccharides like dextrose, C 6 II 12 6 ; disaccha rides include, 

 for example, cane-sugar, C 12 H 22 O u , which breaks up into dextrose and levu- 

 lose, while polysaccharides comprise such bodies as starch and dextrins, which 

 have the formula (C 6 H 10 O 5 ) n . 



In recent years the term glycose has been extended to cover bodies having 

 three to nine carbon atoms and possessing either the constitutiou of an 

 aldehyde-alcohol, — CH(OH)CHO, called aldoses, or of a ketone-alcohol, 

 — COCH 2 OH, called ketoses. These bodies also have hydrogen and oxygen 

 present in a proportion to form water, and the number of carbon atoms always 

 equals in number those of oxygen. According to their number of carbon atoms 

 they are termed trioses, tetroses, pentoses, hexoses, heptoses, octoses. and non< >-i is. 



It has been shown (foot-note, p. 545) how from the asymmetric carbon atom in lactic 

 acid two configurations are derived. If a body (such as trioxybutyric acid) contains two 

 asymmetric carbon atoms, four configurations are possible, 



CH 2 OH CH 2 OH (I I, OH CILOH 



HCOH OHCH OHCH" HCOH 



HIM MI OHCH HCOH OHCH 



COOH COOH COOH COOH 



Similarly among the glycose-aldoses, a triose has two modifications ; a tetrose, four ; a pen- 

 tose, eight: a hexose, sixteen, etc. Thus in the following formula by the variations of H 

 and OH on the four asymmetric carbon atoms, sixteen possible hexoses may be obtained. 



CH 2 OH 



— C— 



— c— 

 — c— 

 -c— 



CHO 



The carbohydrates have well-defined optical properties, rotating polarized light to the 

 right or left, and were therefore originally designated as d- (dextro-) and I- (lsevo-) respec- 

 tively. An inactive (/-) form consists in an equal mixture of the two others; at present, 

 however, thed- may signify a chemical relation to dextrose: thus levulose, which is ordinary 

 fruit sugar and rotates polarized light to the left, is called d- fructose, on account ol its deriva- 

 tion from dextrose. Where the Oil group is attached on the right it may he indicated by 

 the sign +, on the left by — , or the | (Ml may he written below, th< — Oil above. 



II II Oil II 

 orCH.,011 T C (' C (410 

 (Ml OH II (Ml 



Vol. I. 



